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Adarsh Nigam

· started a discussion

· 1 Months ago

Looks like a wrong solution (Question: 193739.0 )

I used the concept like :
V1 = d/t1
v2 = d/t2
here, 'd' is same for both..
so, v1*t1 = v2*t2
36*[5+30/60] = v2*[2+45/60]
=>v2=72km/h

Please correct me if i'm wrong

Question:

Two trains, A and B, start from stations x and y and move towards stations y and x respectively. After passing each other, they take 5 hrs 30 min and 2 hrs 45 min to reach y and x respectively. If the train A is moving at a speed of 36 km/hr, then the speed of the train B is – 

Options:
A) 48.8 km/hr
B) 50.9 km/hr
C) 51 km/hr 
D) 49.3 km/hr 
Solution:
Ans: (b)


Himalaya

· commented

· 1 Months ago

distance is not same because we don't know at which distance they meet. i mean it may be the first one has covered 10 km but second has covered 40 km (just a example).

Adarsh Nigam

· commented

· 1 Months ago

@Knowledge Expert ..How the below formula applies?? What's wrong in the approach that i used(have mentioned in the above comment)??? i want to know the concept...what's wrong with the concept that i used

Knowledge Expert

· commented

· 1 Months ago

Dear Student,

If two trains (or bodies) start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:

(A's speed) : (B's speed) = (√b : √a )

So, 50.9kmph is the correct answer.

Keep learning with us.
All the Best.
Team Toprankers

Abhishek tyagi

· commented

· 1 Months ago

I don't know abt ur method... but i do know a trick to this type of question which goes like this -

speed of A/speed of B = root of [time taken by B/time taken by A]

And the given ans i.e 50.9km/hr is correct...

Shruti Dube

· commented

· 1 Months ago

u r correct...ans should be 72 km/hr
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